Aptitude - Pipes and Cistern - Discussion

Guys, it is very easy.

A tap can fill a tank by 6 hrs. Then one tap is closed after 6 hrs which means 6/2=3 hrs.
Then 3 more taps are opened so now totally there are 4 taps are opened.
We are having remaining time will be 6-3 =3 hrs.
So find 3/4 you get 0. 75 hrs which means 45 mins.
So the Answer will be 3hrs 45 mins.
Hope it will help you.

It is assumed that all the taps are equally efficient, so we have divided 3 hrs, i.e 180 min into 4 equal part, that how 45 min came.

We know Rate * Time = Capacity.

Rate = 1/6 ,
Capacity = 1/2.
1/6 * time =1/2
Here time = 3hrs for capacity half.
Next, more three pipes total of 4 pipes.
4 * 1/6 = 2/3.

Rate for 4 pipes is 2/3, Time=?, Capacity = another 1/2,
2/3 * time = 1/2.
Here time = 3/4 = 0.75hrs(0.75*60min).
Total time = 3hrs + 0.75hrs(45 min).

1/6 part filled by one tap in 1 hr.
1/2 part filled by one tap in 3hrs.
Part filled by 4 taps in 1hr is 4 * (1/6)=2/3.
2/3 part filled by 4 taps in 1 hr.
1/2 part filled by 4 taps in 3/4 hr.
So , total time = 3hr + (3/4)hr.
=3 hr 45 mins(answer).

Time taken by 1tap to fill the tank is 6hrs, then half is 3hrs (work done by 1 tap).
So,
3 * (1/6) + x * (4/6) = 1,
x = 3/4.

They asked total time, so half tank is filled in 3 hour and later it takes 45 min as we calculated. Therefore 3 hour and 45 min.

As we know, rate * time =capacity.

So, after half filled.
A*3=4A *t
t=3/4 hour.
So total time taken is the time taken by A to fill half i.e 3 hr + 3/4 hr = 3 hr 45 minutes.
Thanks.

The half tank filled in 3 hours since the full took 6 hours.
So, the rest half will be filled by 4 tap = 3 * 60/4 = 45.
Complete time to fill the tank = 3 hours 45 min.

Quick one:
1 pipe fills half of the tank=6/=3 hrs.

Remaining half,
1 pipe takes 3 hr.
4 '' '' =3/4 hr= 45 mins.
Total = 3hrs+45mins(Answer)

Time taken by one tap to fill half of the tank = 3 hours.
Part filled by one tap in 1 hour = 1/6,
Part filled by 4 taps together in 1 hour = 4 × 1/6 = 2/3.

Total part filled by one tap + total part filled by 4 taps = 1.
(3)×(1/6) + (x)×(2/3) = 1.
[where x is the time taken by 4 taps to fill the tank].
Solving the equation we get, x = 3/4.
Now,
The Total time taken to fill the tank = 3 hours + 3/4 hours = 15/4 hours, which can also be written as 3(3/4) hours, which is 3 hours 45 minutes.
So, the correct option is (b) 3 hours 45 minutes.